Oracle 18c

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create table your_table (id, value) as
select 1, 'This is the base level - This is level 2 - And this is the second' from dual
union all
select 2, 'Base only' from dual;
2 rows affected

with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1, regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(case when lvl > 1 then rpad(chr(10), lvl, '>') || ' ' end || result)
    within group (order by lvl) as result
from rcte
group by id
order by id;


ID
RESULT


1
This is the base level
> This is level 2
>> And this is the second

2
Base only


with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1, regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(case when lvl > 1 then rpad(' ', lvl, '>') || ' ' end || result)
    within group (order by lvl) as result
from rcte
group by id
order by id;


ID
RESULT


1
This is the base level > This is level 2 >> And this is the second

2
Base only


with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1,
    rpad('>', lvl, '>') || ' ' || regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(result, ' ') within group (order by lvl) as result
from rcte
group by id
order by id;


ID
RESULT


1
This is the base level > This is level 2 >> And this is the second

2
Base only

ID	RESULT
1	This is the base level > This is level 2 >> And this is the second
2	Base only

ID	RESULT
1	This is the base level > This is level 2 >> And this is the second
2	Base only